Is there any information available on whether search engines (Google) count external Javascript or CSS files as backlinks?
Example: Does loading FontAwesome from their CDN count as a backlink for that CDN? Does loading the Bootstrap Javascript files count as backlink for Bootstrap?
Those are not links so they aren't counted as such. They're URLs of resources which are very different things. Hosting such a resource offers no direct SEO value but being known as a reliable host can encourage other sites to link to you as such.
Straight answer NO.
Worth understanding:
Google is pretty good with reading JS and header stuff.
Google may use the signal for page discovery.
In most of the situations those external resources are blocked by the provider, example:
So, from the discovery point of view yes.
